This invention relates to a means for controlling the generation of electrical generating units at interconnected local power plants where the governors respond to increase or decrease signals sent from a central load dispatchers office in accordance with the generation change requirements for the local stations as required to maintain certain conditions in the power system, such as the generation required at each station to maintain its own load at the desired system frequency.
In the control of generation at local power plants the changes in generation called for by the control frequently causes a change in the throttle pressure of the associated boiler system. For example, if there is a call for an increase in output from a generator the control will open the throttle valve to allow increased steam flow from the associated boiler. The increased steam flow will in turn cause a decrease in the steam pressure at the boiler output. When the output of the generator has increased due to the additional steam flow so as to satisfy the requirements of the load dispatcher, the steam pressure will frequently still be at a reduced value as a result of the slow response of the boiler controls to the new requirements. Then, as the steam pressure recovers due to the steam pressure control modifying the boiler inputs, the generation will increase beyond the desired value. That increase will in turn require a readjustment of the governor until there is provided the desired generator output with the steam pressure at its set point.
When there is no control loop at the local station to maintain a tight control on the generation independently of the steam pressure variations, there is required a control system which can compensate for the changes in steam pressure so as to make the generation control independent of the steam pressure variations. It is therefore an object of this invention to provide a control system for controlling the generation of local generators so as to prevent overcorrection by the combustion control system and thus make the generation control more stable by making it insensitive to changes is steam pressure.